docs: def matrix(self):
          """:obj:`numpy.ndarray` of float: The canonical 4x4 matrix
          representation of this transform.
  
          The first three columns contain the columns of the rotation matrix
          followed by a zero, and the last column contains the translation vector
          followed by a one.
          """
          return np.r_[np.c_[self._rotation, self._translation], [[0,0,0,1]]]